A growing body of evidence demonstrates the effects of temperature extremes on health, with considerable research pointing to increased morbidity and mortality associated with extreme heat, particularly in the elderly. Evidence also suggests that, along with demographic shifts, these associations have important implications for public health going forward, as extreme heat events are expected to increase in frequency, intensity, and duration. However, there remain significant gaps in the literature regarding the current and future health impacts of heat, including assessment of sensitive subpopulations and uncertainty quantification in health impact projections. In this project, we will conduct a detailed assessment of heat-related morbidity and climate change health impacts for Atlanta, Georgia. Specifically, we will: 1) assess associations between extreme heat and acute morbidity by age; 2) examine heterogeneity of heat-morbidity associations and spatial patterns of risk by determinants of heat vulnerability; and 3) conduct climate change health impact projections and uncertainty quantification. Approach. Emergency department visit data spanning 20 years (1993-2012) will be acquired from our ongoing study of air quality and acute morbidity in Atlanta. Data on temperature and humidity will be acquired from observing stations in the Atlanta area and various heat metrics, including heat waves, based on temperature and apparent temperature will be defined. In Aim 1, we will assess age-specific short-term associations of extreme heat and heat-related illness, diabetes, renal, and cardiorespiratory morbidity using daily time-series approaches, controlling for air pollution and other time-varying confounders. In Aim 2, we will assess interactions of extreme heat and determinants of heat vulnerability (e.g., age, race, pre- existing diseases, socioeconomic status, and neighborhood green space assessed at the individual- and community-level) on acute health outcomes. Estimated risk ratios will be mapped to evaluate the spatial patterns of heat-related morbidity risk as a function of each heat vulnerability determinant within Atlanta. In Aim 3, using exposure-response functions developed in Aims 1 and 2, we will assess future excess morbidity due to high heat. We will evaluate the sensitivity of the projections to the assumed exposure-response function, population age structure, adaptation scenarios, and outputs from different global and regional climate model combinations, and approaches for calibrating climate model outputs. Expected Results. The anticipated outcomes of our project will be a further understanding of heat-related morbidity, including identification of sensitive subpopulations, intra-urban patterns of risk due to determinants of heat vulnerability, and estimation of future excess heat-related morbidity in Atlanta. These results will ultimately aid in supporting, advancing, and prioritizing targeted intervention efforts and will be valuable for informing emergency preparedness related to climate change. This project will also build the capacity of our team to utilize methods for assessing the impacts of extreme heat, which in the future may be extended to our ongoing work in multiple U.S. cities.